1. Field of the Invention
The present invention relates to an electric rotating machine having a rotor provided with plural permanent magnets, and to a manufacturing method of the electric rotating machine.
2. Description of the Related Art
In a rotor of the conventional electric rotating machines, to facilitate adjustment of magnetic flux amount, a number of claw-shaped magnetic poles covering a rotor coil disposed at a predetermined pitch along the circumferential direction form a pair of pole cores, and the pairs of pole cores are oppositely disposed so that the mentioned claw-shaped magnetic poles are engaged with each other, thus a rotor core being formed.
In the electric rotating machine of this type, a current is applied to a rotor coil to magnetize the pole core. To operate as a generator, a rotating force is applied from outside such as engine to the rotor thereby causing a stator coil to generating an electromotive force. To operate as a motor, a voltage is applied to each of ac terminals of the stator thereby causing the rotor to rotate.
Output of the electric rotating machine in that case relates to an amount of magnetic flux generated in the rotor. That is, main magnetic flux generated by the rotor coil runs through the claw-shaped magnetic poles of the pole core, passing through the stator disposed outside of the pole core, and comes to an adjacent claw-shaped magnetic pole. In this process, in the structure just by engaging the claw-shaped magnetic poles with each other, there exists leakage flux flowing from the side or inner circumferential face thereof to the adjacent claw-shaped magnetic pole. Such leakage flux does not interlink to the stator, and therefore effective magnetic flux amount is reduced, resulting in lowering the output of the electric rotating machine.
To overcome such a disadvantage and improve output of the electric rotating machine, an idea has been heretofore proposed. In this idea, to suppress occurrence of the leakage flux, a permanent magnet is inserted between the claw-shaped magnetic poles adjacent each other along the circumferential direction of the rotor. For example, in the Japanese Patent No.2865091, an annular magnet-holding member formed along the circumferential direction with a recess, into which each claw-shaped magnetic pole of the pole core is fitted, is disposed, and a permanent magnet is held in this magnet-holding member circumferentially at a predetermined pitch, thus forming an assembly. This assembly is mounted on the pole.
In the Japanese Patent No.3144567, another known art is disclosed, and in which each claw-shaped magnetic pole of the pole core is provided with a flange, and combining each pole core forms a magnet fixing part consisting of a pair of flanges. A permanent magnet is inserted into the magnet fixing part from an opening located in axial direction. In addition, a plate is attached before and behind the rotor to prevent the permanent magnet from getting out of the opening of the magnet fixing part.
However, in the former known art as disclosed in the Japanese Patent No.2865091, since a recess into which each claw-shaped magnetic pole of the pole core is inserted is formed along the circumferential direction of the annular magnet holding member, it is essential to minimize a difference between one claw-shaped magnetic pole and another. If there remains any variation between the claw-shaped magnetic poles, it will be impossible to exactly fit the claw-shaped magnetic poles into each recess of the magnet-holding member. In other words, high working accuracy is required in each of the claw-shaped magnetic poles. Therefore it is actually impossible to completely finish the pole core only by forging and it is necessary to apply cutting in order to improve the working accuracy, which results in not only taking much labor but also increase in cost.
Moreover, because of a centrifugal force produced by the rotation of the rotor and applied to the magnet-holding member, it is necessary for the magnet-holding member to have strength to a certain extent. A soft material such as resin easy to mold will be deficient in strength. To cope with this, any material obtained by press working such as spring steel will be essential as the magnet-holding member. However, it is a difficult work configuring a magnet-holding member into an annular shape having recesses, in which the claw-shaped magnetic poles are inserted, along the circumferential direction, which eventually results in much increase in cost.
In the latter known art as disclosed in the Japanese Patent No.3144567, each claw-shaped magnetic pole of the pole core is provided with a flange for mounting a permanent magnet. However, it is difficult to provide the claw-shaped magnetic pole with a flange just by forging, and it is necessary to apply cutting and shaping after assembling. As a result, the pole core becomes expensive.
Moreover, plates are attached before and behind the rotor to prevent the permanent magnet from getting out of the opening of the magnet fixing part. It is certain that the plates are effective in view of preventing the permanent magnet from getting out of, but the plates inhibit the airflow in the vicinity of the rotor. As a result, cooling efficiency of the rotor is lowered resulting in negative affect on the permanent magnet due to heat.
The present invention was made to solve the above-discussed problems and has an object of providing an electric rotating machine capable of preventing effectively generation of leakage flux, manufacturing the rotor relatively easy at reasonable cost without high working accuracy of the pole core and the permanent magnet, and assembling the permanent magnet without negative affect on the cooling efficiency of the rotor. The invention also provides a manufacturing method of such an electric rotating machine.